M2 r cleanup fimsframe

[MOshima-PIFSC]

What is the feature?

• changed parameter names to snake case

How have you implemented the solution?

• nyrs is now n_yrs
• nages is now n_ages
• weightatage is now weight_at_age

I wasn't sure if changing the variable names in test-fimsframe.R was necessary but I went ahead and changed them to be consistent.

• nagecomp is now n_age_comp (in test-fimsframe.R)
• nyears is now n_years (in test-fimsframe.R)
• nindex is now n_index (in test-fimsframe.R)
• agecompdat is now age_comp_dat (in test-fimsframe.R)
• fleet_names_agecomp is now fleet_names_age_comp (in test-fimsframe.R)

Does the PR impact any other area of the project?

Input

slot names are now in snake case

How to test this change

Changes were made in test-fimsframe.R as well.

Developer pre-PR checklist

• [x] I relied on GitHub actions to :test_tube: things for me while I sat on the :couch_and_lamp:.

[github-actions[bot]]

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Checklist

• [ ] The PR is requested to be merged into the appropriate branch (typically main)
• [ ] The code is well-designed.
• [ ] The functionality is good for the users of the code.
• [ ] Any User Interface changes are sensible and look good.
• [ ] The code isn’t more complex than it needs to be.
• [ ] Code coverage remains high, indicating the new code is tested.
• [ ] The developer used clear names for everything.
• [ ] Comments are clear and useful, and mostly explain why instead of what.
• [ ] Code is appropriately documented (doxygen and roxygen).

[kellijohnson-NOAA]

Part of #567